Acrylic materials are used in a wide variety of applications, including buildings, automotive lights, instrument dials, light diffusers, lenses, medical diagnostic devices, signs, and glazing. Acrylic polymers find extensive use in these applications because of their toughness, weatherability, appearance and stability characteristics. Common applications for acrylic compositions include production of sheets for eventual thermoforming into a variety of useful products including, for example, sanitary wares.
Acrylic polymers, including rigid sheets typically have a hydrophobic surface with a water contact angle between 70-80 degrees. Having a hydrophobic surface makes these materials difficult to clean. This is a concern for biomedical and sanitary wares applications.
Certain polymeric materials, e.g. polyvinyl chloride (PVC), polyurethane (PUR) and poly methyl methacrylate (PMMA), are susceptible to biological attack, especially from fungi. In order to reduce or prevent the degradation of plastics resulting from such biological attack, biocidal products have been developed for incorporation into plastics materials or paints to kill the fungi or bacteria responsible or prevent their proliferation.
PMMA and related acrylic copolymers have found widespread use in sanitary ware applications because of their low cost, their low weight compared with metals, and because of their excellent mechanical properties which includes toughness, scratch, and abrasion resistance. Nevertheless, there are some significant limitations of acrylic polymers for these types of applications, and also biomedical applications because of their hydrophobic nature and inability to resist bacteria and fungi growth.
It is known that if pure methyl methacrylate is polymerized, the volume it occupies will shrink typically by about 20% to about 22%. There are also exothermic effects and acceleration in the rate of polymerization which make the reaction difficult to control. Accordingly, it has become common commercially to pre-polymerize a portion of the monomer and prepare a solution of such pre-polymerized methyl methacrylate in additional monomer so the casting, or final polymerizing, process can be more readily controlled and its ultimate size and shape anticipated. Such casting, and stationary or cell casting, has been performed with minor amounts of other monomers in the methyl methacrylate, such as ethyl or butyl acrylate, di-unsaturated cross-linking agents, and the like.
Various organic and inorganic additives or fillers are and have been used in resinous articles for decorative, strength, fire-retardant, economic and other reasons. Pigments may be added for color, glass fibers for strength, aluminum trihydrate for fire retarding, and any inexpensive space-occupier for economic reasons mixtures are also described and a method of measuring swellability is given.
It may also be considered relevant to the background of this invention that impact resistance has been imparted to poly methyl methacrylate sheet and other products by incorporating into the acrylic sheet an effective amount of an impact modifier additive which is in the form of small beads or particles made of acrylic esters but also including butyl acrylate or other higher acrylate to form a rubbery component in the particle.